1. Field of the Invention
This invention relates in general to the use of light-sensitive polymeric compositions in the graphic arts to produce photomechanical images and in particular to improvements in the image-forming development of positive-working photoresist films and positive-working lithographic printing plates containing light-sensitive quinone diazides. More specifically, this invention relates to the use of certain developing compositions which provide improved results in the development of the aforesaid photoresist films and printing plates.
2. Description of the Prior Art
An important class of light-sensitive materials that is widely utilized in the graphic arts in the formation of photomechanical images is the class of quinone diazides. These materials enjoy extensive use in such important applications as positive-working photoresist films and positive-working lithographic printing plates. Exposure of the composition to actinic radiation results in a solubility differential between the exposed and unexposed areas such that treatment with an appropriate developer results in removal of the radiation struck areas and retention of the desired image areas on the support. It is believed that such exposure decomposes the diazo structure in the radiation struck areas to form the free carboxylic acid group, thereby rendering the exposed areas soluble in alkaline developer solutions. The developer solutions which are employed for this purpose can be aqueous solutions or organic solutions. Typical examples of alkaline developer solutions utilized heretofore in development of quinone diazide compositions include solutions of sodium hydroxide, ammonium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate or sodium phosphate. Developers containing lower alcohols, ketones, or amines such as the alkyl amines, cycloalkyl amines and alkanolamines, are also well known.
It is known to use quaternary ammonium hydroxide developing agents in developer compositions that are employed in developing light-sensitive quinone diazide compositions. Thus, for example, the use of tetraalkylammonium hydroxides, such as tetramethylammonium hydroxide or tetraethylammonium hydroxide, as developing agents is described in Japanese Patent Publication No. 56226/1976 published May 17, 1976. Use of tetramethylammonium hydroxide as a developing agent is also described in British Pat. No. 1,367,830. Especially useful quaternary ammonium hydroxide developing agents are the quaternary alkanol ammonium hydroxides such as, for example, the methyltriethanolammonium hydroxide of U.S. Pat. No. 4,141,733. As described in this patent, this developing agent is particularly advantageous for use in forming a metal-ion-free developer composition that is especially adapted for forming fine image detail in the utilization of photoresists in the manufacture of integrated circuit devices. Developer compositions containing methyltriethanolammonium hydroxide provide many highly advantageous characteristics such as extended development latitude, increased exposure latitude, improved resist contrast, improved prebake latitude, a low depletion rate and minimal loss of image layer thickness.
While developer compositions containing a quaternary alkanol ammonium hydroxide developing agent are excellent developers for resists of the quinone diazide type, they suffer from a serious problem in that gradual decomposition of the quaternary alkanol ammonium hydroxide compound, with consequent darkening of the composition and changes in its performance as a developer, tends to take place. A solution to this problem is provided in U.S. Pat. No. 4,294,911. The solution is the incorporation in the developing composition of a stabilizing concentration of a sulfite, for example, ammonium sulfite. Sulfites function very effectively as stabilizing agents, that is, as agents which serve to prevent or retard darkening of the composition and changes in its performance as a developer for quinone diazide compositions. As explained in U.S. Pat. No. 4,294,911, it is believed that quaternary alkanol ammonium hydroxide developing agents can decompose to form aldehydes and that the aldehydes can polymerize to form polyaldehydes, which are highly colored materials that result in a gradual darkening of the composition. Depending on the particular conditions involved, the polyaldehydes can be dimers, trimers, oligomers or low molecular weight polymers. Sulfites are believed to form adducts with the aldehydes and thereby prevent the formation of the polyaldehydes.
While the use of sulfites as stabilizing agents represents an important advance in the art, it is subject to a serious disadvantage which has hindered the commercial utilization of developing compositions containing quaternary alkanol ammonium hydroxide developing agents. Such developing compositions are typically prepared, shipped and stored as concentrates and are diluted by the user to the proper concentration. In the preparation and use of such concentrates, it is essential to be able to accurately determine the total solution alkalinity (such term being used herein to refer to alkalinity contributed by the quaternary alkanol ammonium hydroxide as well as by any other basic ingredients in the solution) so as to be able to accurately establish the degree of dilution necessary to provide a working strength developing solution of a particular pH. The activity of these developing solutions is, in part, dependent on pH and the optimum pH in a given situation will depend on various factors, such as the particular ingredients in the light-sensitive composition, the particular ingredients in the developing composition, the type of equipment utilized in exposing the light-sensitive composition, the development temperature, and so forth. Thus, there is a critical need for a simple and effective method of accurately determining the total solution alkalinity of the concentrate. A particularly convenient way of doing this is by titration with an acid, for example, hydrochloric acid. However, it has been found that if a sulfite is used as a stabilizing agent, it interferes with the titration and renders it impossible to accurately determine the total solution alkalinity by a titration process. The exact mechanism whereby such interference occurs is not known, but it has been found through repeated experimentation that significantly different results are obtained when titrating otherwise identical developing compositions depending on whether or not a sulfite is present in the composition. Thus, the use of a sulfite as a stabilizing agent leads to false readings for total solution alkalinity.
It is toward the objectives of providing a developer composition that is stable, so that its performance does not change significantly with the passage of time, i.e., a developer composition that has a relatively long "shelf-life," and of providing a developer composition whose total solution alkalinity can be accurately determined by titration, that the present invention is directed.